1. Field of the Invention
The present invention relates to an electric steering lock apparatus for locking a steering shaft of a vehicle.
2. Description of the Related Art
As this type of conventional electric steering lock apparatuses, there have been proposed various apparatuses as shown in, for example, Japanese Patent Application Laid-Open No. 2002-205622. When an electric steering lock apparatus is arranged using a cam member, the apparatus is mainly composed of a rotation shaft driven by a drive source, the cam member, which is fixed to the rotation shaft and rotates in an unlocking direction and in a locking direction together with the rotation shaft, a lock member, which has a cam abutment surface abutting against the sliding surface of the cam member and shifts between a lock position at which the rotation of a steering shaft is locked and an unlock position at which the rotation of the steering shaft is permitted following to the sliding surface of the cam member, and a spring for urging the lock member to the lock position.
In the above arrangement, when a vehicle parks, the lock member is located at the lock position to thereby lock the steering shaft. With this arrangement, the vehicle can be protected against theft when it parks.
When the parked vehicle is to be driven, the cam member is rotated in the unlocking direction by the drive source, thereby the lock member is shifted to the unlock position so that the steering shaft is free to rotate.
Incidentally, in the electric steering lock apparatus, although the lock member must be held at the unlock position at all times unless the vehicle parks, the following disadvantages arise when the relation between the rotating position of the cam member and the position of the center of gravity thereof and the relation between the contact position at which the cam member comes into contact with the lock member, and the center of rotation of the cam member are not taken into consideration.
That is, when the position of the center of gravity of the cam member is eccentric with respect to the center of rotation thereof and the rotation torque resulting from the own weight of the cam member acts in the locking direction at the position of the cam member at which the lock member is located at the unlock position, there is a possibility that the cam member is rotated in the locking direction by the rotation torque resulting from the own weight of the cam member and that the lock member is shifted to the lock position. Further, when the contact position at which the lock member comes into contact with the cam member is eccentric with respect to the center of rotation of the cam member and thus the rotation torque resulting from the external force from the lock member acts in the locking direction at the position of the cam member at which the lock member is located at the unlock position, there is a possibility that the cam member is rotated in the locking direction by the rotation torque resulting from the external force and the lock member is shifted to the lock portion.